Continuously variable transmission control method and apparatus

ABSTRACT

A method and apparatus for controlling a continuously variable transmission having an input and output shaft for use with an automotive vehicle. The transmission is operable at a variable speed ratio for transmitting a drive from the input shaft to the output shaft. A target value for the speed of rotation of the input shaft of the transmission is calculated based on the sensed vehicle operating conditions including vehicle acceleration (deceleration). A correction factor per predetermined unit time is calculated based on the vehicle acceleration (deceleration) when the vehicle acceleration (deceleration) exceeds a threshold value with the accelerator pedal being released. The correction factor is used to correct the target input shaft speed value at intervals of the predetermined unit time. The speed ratio is controlled to bring the input shaft speed into coincidence with the corrected target value.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for controlling acontinuously variable transmission for use with an automotive vehicle tochange the engine brake force when the vehicle is coasting on a slopehaving a changing gradient.

Some automotive vehicles employ a continuously variable transmissionhaving an input shaft coupled to the engine and an output shaft coupledto the drive shaft for transmitting a drive from the engine to the driveshaft. Such a continuously variable transmission operates with a speedratio controlled in a manner to bring the speed of rotation of the inputshaft into coincidence with a target value calculated as a function ofengine throttle position (or accelerator pedal position) and vehiclespeed. It is the current practice to decrease the target input shaftspeed value as the throttle position decreases, If the vehicle iscoasting on a downhill slope, the operator will release the acceleratorpedal. This causes the throttle position to decrease so that the targetinput shaft speed value is changed (decreased) in a direction to weakenthe engine brake. As a result, the operator would feel an excessivedegree of vehicle acceleration in spite of the fact that the acceleratorpedal is released and increase the frequency at which the operatordepresses the brake pedal.

For example, Japanese Patent Kokai No. 6-81932 discloses a continuouslyvariable transmission control apparatus intended to reduce the frequencyat which the operator depresses the brake pedal when the vehicle iscoasting on a downhill slope by setting a great lower limit for thetarget input shaft speed value to perform aggressive operate enginebrake operations. With such a conventional apparatus, however, thetarget input shaft speed value changes frequently to provide a sense ofincompatibility to the operator with changes in the gradient of theslope.

SUMMARY OF THE INVENTION

It is a main object of the invention to provide an improved continuouslyvariable transmission control method and apparatus which can provide asmooth engine brake force change to meet the operators expectationtherefor when the vehicle is coasting on a slope having a changinggradient with the accelerator pedal being released.

There is provided, in accordance with the invention, an apparatus forcontrolling a continuously variable transmission for use with anautomotive vehicle including an accelerator pedal. The transmission hasan input and output shaft. The transmission is operable at a variablespeed ratio for transmitting a drive from the input shaft to the outputshaft. The continuously variable transmission control apparatuscomprises means for sensing vehicle operating conditions includingvehicle acceleration, means for producing a released accelerator pedalindicative signal when the accelerator pedal is released, means forcalculating a target value for the speed of rotation of the input shaftbased on the sensed vehicle operating conditions, means for calculatinga correction factor per predetermined unit time based on the sensedvehicle acceleration when the sensed vehicle acceleration exceeds athreshold value in the presence of the released accelerator pedalindicative signal, means for adding the correction factor to the targetinput shaft speed value to correct the target input shaft speed value atintervals of the predetermined unit time, and means for controlling thespeed ratio to bring the input shaft speed into coincidence with thecorrected target value.

In another aspect of the invention, the continuously variabletransmission control apparatus comprises means for sensing vehicleoperating conditions including vehicle deceleration, means for producinga released accelerator pedal indicative signal when the acceleratorpedal is released, means for calculating a target value for the speed ofrotation of the input shaft based on the sensed vehicle operatingconditions, means for calculating a correction factor per predeterminedunit time based on the sensed vehicle deceleration when the sensedvehicle deceleration exceeds a first threshold value in the presence ofthe released accelerator pedal indicative signal, means for subtractingthe correction factor from the target input shaft speed value todecrease the target input shaft speed value at intervals of thepredetermined unit time, and means for controlling the speed ratio tobring the input shaft speed into coincidence with the decreased targetvalue.

In another aspect of the invention, there is provided a method ofcontrolling a continuously variable transmission for use with anautomotive vehicle including an internal combustion engine, anaccelerator pedal and a drive shaft. The transmission has an input shaftcoupled to the engine and an output shaft coupled to the drive shaft.The transmission is operable at a variable speed ratio for transmittinga drive from the engine to the drive shaft. The continuously variabletransmission control method comprises the steps of sensing vehicleoperating conditions including vehicle acceleration, producing areleased accelerator pedal indicative signal when the accelerator pedalis released, calculating a target value for the speed of rotation of theinput shaft based on the sensed vehicle operating conditions,calculating a correction factor based on the sensed vehicle accelerationwhen the sensed vehicle acceleration exceeds a threshold value in thepresence of the released accelerator pedal indicative signal, adding thecorrection factor to the target input shaft speed value to correct thetarget input shaft speed value, controlling the speed ratio to bring theinput shaft speed into coincidence with the corrected target value, andcontinuously repeating the above sequence of steps at uniform intervalsof time to effect changes in the target input shaft speed value inresponse to changes in the vehicle acceleration.

In still another aspect of the invention, the continuously variabletransmission control method comprises the steps of sensing vehicleoperating conditions including vehicle deceleration, producing areleased accelerator pedal indicative signal when the accelerator pedalis released, calculating a target value for the speed of rotation of theinput shaft based on the sensed vehicle operating conditions,calculating a correction factor based on the sensed vehicle decelerationwhen the sensed vehicle acceleration exceeds a first threshold value inthe presence of the released accelerator pedal indicative signal,subtracting the correction factor to the target input shaft speed valueto decrease the target input shaft speed value, controlling the speedratio to bring the input shaft speed into coincidence with the decreasedtarget value, and continuously repeating the above sequence of steps atuniform intervals of time to effect changes in the target input shaftspeed value in response to changes in the vehicle deceleration.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail by reference to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a block diagram showing one embodiment of a continuouslyvariable transmission control apparatus made in accordance with theinvention;

FIG. 2 is an overall flow diagram showing the operation of the digitalcomputer used for the continuously variable transmission control;

FIG. 3 is a detailed flow diagram showing the programming of the digitalcomputer as it is used for target input shaft speed calculation;

FIGS. 4 to 10 are detailed flow diagrams showing the programming of thedigital computer as it is used for target input shaft speed calculation;

FIG. 11 is a graph of vehicle speed versus input shaft speed;

FIG. 12 is a graph of vehicle speed versus vehicle acceleration; FIG. 13is a graph of vehicle acceleration versus input shaft speed correctionfactor;

FIG. 14 is a graph of vehicle acceleration versus input shaft speedcorrection factor;

FIG. 15 is a graph used in explaining the operation of the speed changecontrol apparatus of the invention when the vehicle is coasting on adownhill slope having a changing gradient;

FIG. 16 is a graph of vehicle speed versus operators expecteddeceleration;

FIG. 17 is a graph of vehicle acceleration versus input shaft speedcorrection factor; and

FIG. 18 is a graph used in explaining the operation of the speed changecontrol apparatus of the invention when the vehicle is coasting on aroad changing from a downhill slope to an uphill slope.

DETAINED DESCRIPTION OF THE INVENTION

With reference to the drawings, and in particular to FIG. 1, there isshown a continuously variable transmission control apparatus for usewith an automotive vehicle having an internal combustion engine 1. Theengine 1 operates on command from an engine control unit 6 whichcontrols the amount of fuel metered to the engine 1, the fuel-injectiontiming and the ignition-system spark-timing. For example, the amount offuel metered to the engine, this being determined by the width of theelectrical pulses applied to the fuel injector 4, is repetitivelydetermined from calculations performed in the engine control unit 6based on various conditions of the engine that are sensed during itsoperation. These sensed conditions include cylinder-head coolanttemperature, ambient temperature, throttle position, engine load, enginespeed, etc. The calculated value for the fuel-injection pulse-width istransferred to set the fuel injector 4 according to the calculated valuetherefor. A drive from the engine 1 is transmitted to a drive shaft 3through a continuously variable transmission 2. The continuouslyvariable transmission 2 has an input shaft coupled to an internalcombustion engine 1 and an output shaft coupled to the drive shaft 3.The continuously variable transmission 2 may be of the V-belt or troidaltype.

The continuously variable transmission 2 operates on command applied toa speed ratio control unit 5 from a transmission control unit 7. Thetransmission control unit 7 determines a target input shaft speed DSRREVrepetitively from calculations performed therein based on variousconditions of the automotive vehicle that are sensed during itsoperation. These sensed conditions include vehicle speed VSP, throttleposition TVO, transmission input shaft speed Ni, driven road wheelspeed, brake pedal position, transmission output shaft speed No, vehiclelongitudinal acceleration G and accelerator pedal position. Thus, avehicle speed sensor 8, a throttle position sensor 9, an engine speedsensor 10, a driven road wheel speed sensor 11, a brake switch 12, atransmission output shaft speed sensor 13, a vehicle acceleration sensor14 and an idle switch 15 are connected to the transmission control unit7. The vehicle speed sensor is provided to sense the speed VSP oftraveling of the automotive vehicle. The throttle position sensor 9 maybe a potentiometer associated with the throttle valve situated in theinduction passage of the engine and connected in a voltage dividercircuit for supplying a voltage proportional to the degree TVO ofopening of the throttle valve. The engine speed sensor 10 is providedfor producing a pulse signal having a repetition rate proportional tothe speed Ne of rotation of the engine. The driven road wheel speedsensor 11 is located for producing a pulse signal having a repetitionrate proportional to the speed of rotation of the driven road wheels.The brake switch 12 is responsive to the application of braking to theautomotive vehicle to close to supply current from the engine battery tothe transmission control unit 7. The transmission output shaft speedsensor 13 is located for producing a pulse signal of a repetition rateproportional to the speed of rotation of the transmission output shaft.The vehicle acceleration sensor 14 is provided for producing a signalindicative of the longitudinal acceleration G of the automotive vehicle.The idle switch 15 closes to supply current from the engine battery tothe transmission control unit 7 when the throttle position is at anangle less than a predetermined value, that is, the accelerator pedal isreleased. The continuously variable transmission is shown as having aninput shaft directly coupled to the engine 1. In this case, the speed Niof rotation of the transmission input shaft is equal to the engine speedNe. It is to be understood, of course, that the transmission input shaftmay be coupled to the engine 1 through a reduction gear unit or torqueconverter. In this case, another speed sensor is provided to produce asignal indicative of the speed Ni of rotation of the transmission inputshaft. The transmission control unit 7 also communicates with the enginecontrol unit 6 for synchronized engine and transmission control. Thetransmission control unit 7. The determined target input shaft speedDSRREV is converted into a corresponding target speed ratio DSRRTO whichis transferred to the speed ratio control unit 5 to bring the inputshaft speed Ni into coincidence with the target input shaft speedDSRREV.

The transmission control unit 7 may employ a digital computer whichincludes a central processing unit (CPU) a central processing unit(CPU), a read only memory (ROM), a random access memory (RAM) and aninput/output interface unit (I/O). The central processing unitcommunicates with the rest of the computer. The input/output interfaceunit includes an analog-to-digital converter which receives analogsignals from the throttle position sensor 9 and other sensors andconverts them into digital form for application to the controlprocessing unit. The input/output interface unit also includes counterswhich count the pulses fed thereto from the speed sensors 10, 11 and 13and convert the counts into corresponding speed indication digitalsignals for application to the central processing unit. The read onlymemory contains the programs for operating the central processing unitand further contains appropriate data in look-up tables used incalculating appropriate values for the speed ratio control.

FIG. 2 is a flow diagram illustrating the programming of the digitalcomputer as it is used to control the continuously variable transmission2. The computer program is entered at the point 102 at uniform intervalsof time, for example 5 msec. At the point 104 in the program, the sensorsignals fed to the transmission control unit 7 from various sensors 8 to15 are read into the computer memory. At the point 106, a target valueDSRREV for the speed Ni of rotation of the transmission input shaft iscalculated from a speed change map programmed into the computer. Thespeed change map defines the target input shaft speed DSRREV as afunction of throttle position TVO and vehicle speed VSP, as shown inFIG. 11. At the point 108, the calculated target input shaft speed valueDSRREV is corrected for engine brake operation. This correction is madebased on the vehicle longitudinal acceleration G as described later ingreater detail. At the point 110 in the program, a target speed ratioDSRRTO is calculated to bring the transmission input shaft speed Ni incoincidence with the corrected target value DSRREV. At the point 112,the calculated target speed ratio value DSRRTO is transferred to theinput/output interface unit which converts it into a correspondingcontrol signal. This control signal is applied to the speed ratiocontrol unit 5 which thereby operates the transmission 2 with a speedratio corresponding to the calculated value DSRRTO.

FIG. 3 is a flow diagram illustrating the above correction of the targettransmission input shaft speed value DSRREV. At the point 120 in FIG. 3,which corresponds to the point 108 of FIG. 2, the computer program isentered. At the point 122, an acceptable correction range where thespeed Ni of the input shaft of the continuously variable transmission 2can be corrected is determined based on the target input shaft speedDSRREV calculated at the point 106 of FIG. 2. At the point 124, athreshold value of the vehicle longitudinal acceleration G iscalculated. At the point 126, the vehicle acceleration G is comparedwith the calculated threshold value for a determination as to whether ornot a stronger or weaker engine brake is required. At the point 128, therate of change of the engine brake force, that is, a correction factorby which the target input shaft speed is to be corrected per unit time,is calculated according to the vehicle longitudinal acceleration G. Atthe point 130, the correction factor calculated at the point 128 is usedto correct the target input shaft speed DSRREV so as to produce anengine brake force corresponding to the vehicle longitudinalacceleration. At the point 132, the corrected target input shaft speedDSRENBR is set as a new target input shaft speed DSRREV. The new targetinput shaft speed DSRREV is outputted to calculate a target speed ratioDSRRTO. Following this, the program proceeds to the point 134 where theprogram returns to the entry point 120.

Referring to FIGS. 4 to 10; the details of the above correction of thetarget transmission input shaft speed value DSRREV will be described. Atthe point 140 in FIG. 4, which corresponds to the point 122 of FIG. 3,the computer program is entered. At the point 142 in the program, anupper limit DSRHLMT of the acceptable correction range for the inputshaft speed Ni is calculated from the map of FIG. 11 which defines theupper limit DSRHLMT as a function of vehicle speed VSP. At the point144, a lower limit DSRLLMT of the acceptable correction range for theinput shaft speed Ni is calculated from the map of FIG. 11 which definesthe lower limit DSRLLMT as a function of vehicle speed VSP. At the point146, an acceleration side threshold value VSPOVLM is calculated from amap programmed into the computer. This map defines the acceleration sidethreshold value VSPOVIM as a function of vehicle speed VSP, as shown inFIG. 12. At the point 148, a deceleration side threshold value VSPUDLMis calculated from the map of FIG. 12. The map may be obtainedexperimentally from accelerations the operator expects when theaccelerator pedal is released, this being detected when the idle switch15 is turned on. The operator bodily senses vehicle acceleration in anaccelerated motion range (AMR) defined above the acceleration sidethreshold value VSPOVLM and vehicle deceleration in a decelerated motionrange (DMR) defined below the deceleration side threshold value VSPUDLM.Upon completion of the step at the point 148 in the program of FIG. 4,the program proceeds to the point 150 of FIG. 5 which corresponds to thepoint 126 of FIG. 3. At the point 152, a determination is made as towhether or not the vehicle speed VSP is equal to or less than apredetermined value, for example, 10 Km/h. If the answer to thisquestion is “yes” then it means that the vehicle speed is in apredetermined low speed rnage and the program proceeds to the point 154where the vehicle acceleration TKRAMS6 is set at 0 and then to the point166. Otherwise, the program proceeds to the point 156 where the vehicleacceleration (or deceleration) TKRAMS6 is calculated based on thedifference between the vehicle speed VSP read in this cycle of executionof this program and the vehicle speed VSP₋₅ read before a predeterminednumber of (in this case 5) cycles of execution of this program. Althoughthe vehicle acceleration TKRAMS6 is calculated as the rate of change ofthe vehicle speed VSP, it is to be understood, of course, that it may bethe sensed value of the vehicle acceleration sensor 14. At the point158, a determination is made as to whether or not the vehicleacceleration TKRAMS6 is greater than the acceleration side thresholdvalue VSPOVLM calculated at the point 146 of FIG. 4. If the answer tothis question is “yes”, then the program proceeds to the point 160 wherean accelerated motion flag VSPPLS is set to indicate that the vehicleacceleration is in the accelerated motion range so that a strongerengine brake is required and then to the point 168. Otherwise, theprogram proceeds to another determination step at the point 162. Thisdetermination is as to whether or not the vehicle acceleration TKRAMS6is smaller than the deceleration side threshold value VSPUDLM calculatedat the point 148 of FIG. 4. If the answer to this question is “yes”,then the program proceeds to the point 164 where a decelerated motionflag VSPMNS is set to indicate that the vehicle acceleration is in thedecelerated motion range requiring a weaker engine brake force and thento the point 168. Otherwise, the program proceeds to the point 166 wherea uniform motion flag VSPEOS is set to indicate that the vehicleacceleration is in the uniform motion range so that the existing enginebrake is to be retained.

Following this, the program proceeds to the point 168 of FIG. 6 whichcorresponds to the point 128 of FIG. 3. At the points 170 and 172 in theprogram, a down- or up-shift correction factor DDSRDN or DDSRUP by whichthe target input shaft speed DSRREV is to be corrected per unit time iscalculated from a map programmed into the computer. This map specifiesthis correction factor DDSRDN or DDSRUP as a function of vehicleacceleration TKRAMS6, as shown in FIG. 13, This map may be obtainedexperimentally, as described later. The downshift correction factorDDSRDN is calculated in a direction to increase the target input shaftspeed value DSRREV so as to increase the engine brake force when thevehicle acceleration TKRAMS6 has a positive sign and the up-shiftcorrection factor DDSRUP is calculated in a direction to decrease thetarget input shaft speed value DSRREV so as to decrease the engine brakeforce when the vehicle acceleration TKRAMS6 has a negative sign. In theillustrated case, the unit time corresponds to the time interval (5msec) of execution of this program.

At the point 174 in the program, a determination is made as to whetheror not a flag OLDIDLR, which was set to 1 if the idle switch 15 is offin the last cycle of execution of this program, is 0. If the answer tothis question is “yes” then the accelerator pedal was depressed and theprogram proceeds to another determination step at the point 176. Thisdetermination is as to whether or not a flag IDLE, which has been set to1 if the idle switch 15 is off in the present cycle of execution of thisprogram, is 0. If the answer to this question is “yes” then it meansthat the accelerator pedal remains depressed and the program proceeds tothe point 220 of FIG. 8. Otherwise, it means that the accelerator pedalis released from its depressed position and the program proceeds to thepoint 178 where the flag OLDIDLE is set to 1 and then the programproceeds to the point 240 of FIG. 9.

If the answer to the question inputted at the point 174 is “no” then itmeans that the accelerator pedal was released and the program proceedsto another determination step at the point 180. This determination is asto whether or not the flag IDLE is 0. If the answer to this question is“no”, then it means that the accelerator pedal remains released and theprogram proceeds to the point 200 of FIG. 7. Otherwise, it means thatthe accelerator pedal is depressed from its released position and theprogram proceeds to the point 182 where the flag OLDIDLE is cleared to 0and then to the point 220 of FIG. 8.

FIG. 7 is a flow diagram illustrating the correction of the target inputshaft speed value DSRREV when the accelerator pedal remains released. Atthe point 202 in the program, a determination is made as to whether ornot the accelerated motion flag VSPPLS (FIG. 5) has been set at 1. Ifthe answer to this question is “yes” then it means that the vehicleacceleration is in the accelerated motion range (FIG. 12) and theprogram proceeds to the point 204 where the central processing unitincrease the target input shaft speed value DSRREV by adding thedownshift correction factor DDSRDN calculated at the point 170 of FIG. 6to the last corrected target input shaft speed value DSRENBR(DSRENBR=DSRENBR₋₁+DDSRDN where DSRENBR₋₁ is the corrected target inputshaft speed value obtained in the last cycle of execution of thisprogram) in order to increase the engine brake force so as to bring thevehicle acceleration from the accelerated motion range into the uniformmotion range. At the point 206, a correction flag NOWCNT is set at 1 toindicate that the target input shaft speed value DSRREV is beingcorrected. Following this, the program proceed to the point 250 of FIG.10.

If the answer to the question inputted at the point 202 is “no”, thenthe program proceeds to another determination step at the point 208.This determination is as to whether or not the correction flag NOWCNThas been set. If the answer to this question is “no”, then it means thatno correction is required for the target input shaft speed value DSRREVand the program proceeds to the point 210 where the target input shaftspeed value DSRREV calculated at the point 106 of FIG. 2 is set for thecorrected target input shaft speed value DSRENBR. Following this, theprogram proceeds to the point 250 of FIG. 101

If the answer to the question inputted at the point 208 is “no”, thenthe program proceeds to another determination step at the point 212.This determination is as to whether or not the decelerated motion flagVSPMNS (FIG. 5) has been set. If the answer to this question is “yes”,then it means that the vehicle acceleration is in the decelerated motionrange and the program proceeds to the point 214. Otherwise, the programproceeds to the point 250 of FIG. 10. At the point 214, a determinationis made as to whether or not the brake pedal is released. Thisdetermination is made based on the signal BRK fed from the brake switch12. If the answer to this question is “yes” (BRK=0), than the programproceeds to the point 216 where the central processing unit decreasesthe target input shaft speed value DSRREV gradually by adding theup-shift correction factor DDSRUP (negative value) calculated at thepoint 172 of FIG. 6 to the last corrected target input shaft speed valueDSRENBR (DSRENBR=DSRENBR₋₁+DDSRUP where DSRENBR₋₁ is the correctedtarget input shaft speed value DSRENBR obtained in the last cycle ofexecution of this program). Following this, the program proceeds to thepoint 250 of FIG. 10. If the answer to the question inputted at thepoint 214 is “no”, then the program proceeds to the point 250 of FIG.10. That is, the operators braking operation is given top priority bypreventing the target input shaft speed value DSRREV from beingcorrected to a smaller value even though the vehicle acceleration is inthe decelerated motion range where the engine brake should be weakened.

FIG. 8 is a flow diagram illustrating the correction of the target inputshaft speed value DSRREV when the accelerator pedal is depressed orremains depressed. At the point 222 in the program, a determination ismade as to whether or not the correction flag NOWCNT has been set at 1.If the answer to this question is “yes”, then it means that the targetinput shaft speed value DSRREV is being corrected and the programproceeds to the point 228. Otherwise, the program proceeds to the point224 where the correction flag NOWCNT is cleared to 0 and then to thepoint 226 where the target input shaft speed value DSRREV calculated atthe point 106 of FIG. 2 is set for the corrected target input shaftspeed value DSRENBR. Following this, the program proceeds to the point270 of FIG. 10.

At the point 228 in the program, a determination is made as to whetheror not the target input shaft speed value DSRREV calculated at the point106 of FIG. 2 is equal to or less than the corrected target input shaftspeed value DSRENBR₋₁ obtained in the last cycle of execution of thisprogram. If the answer to this question is “yes”, then the programproceeds to the point 230. Otherwise, the program proceeds to the point224. At the point 230, the corrected target input shaft speed valueDSRENBR is calculated by subtracting a predetermined value (in theillustrated case 1 rmp) from the last corrected target input shaft speedvalue DSRENBR₋₁ (DSRENBR=DSRENBR₋₁ −1). Following this, the programproceeds to the point 270 of FIG. 10.

FIG. 9 is a flow diagram illustrating the correction of the target inputshaft speed value DSRREV when the accelerator pedal is released. At thepoint 242 in the program, a determination is made as to whether or notthe last corrected target input shaft speed value DSRENBR₋₁ is greaterthan the upper limit DSRHLMT for the input shaft speed calculated at thepoint 142 of FIG. 4. If the answer to this question is “yes”, then theprogram proceeds to the point 244 where the upper limit. DSRHLMT is setfor the corrected target input shaft speed DSRENBR and then to the point250 of FIG. 10. Otherwise, the program proceeds to another determinationstep at the point 246. This determination is as to whether or not thecorrection flag NOWCNT has been set at 1. If the answer to this questionis “yes”, then it means that the target input shaft speed value DSRREVis being corrected and the program proceeds to the point 250 of FIG. 10.Otherwise, the program proceeds to the point 228 where the target inputshaft speed value DSRREV calculated at the point 106 of FIG. 2 is setfor the corrected target input shaft speed value DSRENBR. Followingthis, the program proceeds to the point 250 of FIG. 10.

At the point 252 in the program of FIG. 10, a determination is made asto whether or not the corrected target input shaft speed value DSRENB isequal to or less than the lower limit DSRLLIT calculated at the point144 of FIG. 4. If the answer to this question is “yes”, then the programproceeds to the point 254 where the lower limit DSRLLMT is set for thecorrected target input shaft speed value DSRENBR. At the point 256, thecorrection flag is cleared to zero. Following this, the program proceedsto the point 272.

If the answer to the question inputted at the point 254 is “no”, thenthe program proceeds to another determination step at the point 258.This determination is as to whether or not the corrected target inputshaft speed value DSRENBR is greater than the upper limit DSRHLMTcalculated at the point 142 of FIG. 4. If the answer to this question is“yes”, then the program proceeds to the point 266. Otherwise, theprogram proceeds to the point 272. At the point 266, the upper limitDSRHLMT is set for the corrected target input shaft speed value DSRENBR.Upon completion of the step at the point 266, the program proceeds tothe point 272. The program proceeds from the point 270 to the point 272.

At the point 272, the corrected target input shaft speed value DSRENBRis set for the new target input shaft speed value DSRREV. Followingthis, the program proceeds to the point 274 where the program returns tothe entry point 102 of FIG. 2. The calculated new target input shaftspeed value DSRREV is transferred to the input/output interface unitwhich converts it into a corresponding target speed ratio and produces acontrol signal causing the speed ratio control unit 5 to set thecontinuously variable transmission 2 according to the target speedratio.

Test were performed on a given automotive vehicle coasting down hillswith the accelerator pedal released to determine the optimum desiredrelationships between downshift correction factors DDSRDN and vehicleaccelerations. The test results indicate that the degree of decelerationthe operator expects changes according to the vehicle acceleration. Themap of FIG. 13 from which the down- and up-shift correction factorsDDSRDN and DDSRUP are calculated is prepared in view of the testresults.

The calculation of the downshift correction factor DDSRDN will bedescribed further with reference to FIG. 14. The bold lines indicatechanges in the down-shaft correction factor DDSRDN in connection withvalues set in direct proportion to the vehicle acceleration, asindicated by the broken line. FIG. 14 shows the acceleration regionwhere the vehicle acceleration is positive as divided into a smallacceleration range A where the vehicle acceleration is less than apredetermined value near zero, an intermediate acceleration range B anda great acceleration range C. The small acceleration range A ischaracterized by the fact that the operator is bothered with frequentengine speed (target input shaft speed) changes, the operator feels asense of incompatibility with the downshift correction factor DDSRON setin direct proportion to the vehicle acceleration, indicated by thebroken line of FIG. 14, and the operator does not expect vehicledeceleration even when the accelerator pedal is released. Thus, it isdesirable in the small acceleration range A to set the downshiftcorrection factor DDSRDN almost at zero. The intermediate accelerationrange B is characterized by the fact that the operator requires a rapidengine brake increase and is impatient with a delay of engine brakeapplication because of gradually increasing engine speeds. Thus, it isdesirable in the intermediate acceleration range B to realize rapidengine brake application by increasing the downshift correction factorDDSRDN, as indicated by the bold lines of FIG. 14. The greatacceleration range C is characterized by the fact that the operatorrequires a great engine brake force because of rapid vehicle speedincreases. The operator does not feel any sense of incompatibility evenfor an excessive degree of deceleration and feels uneasy for aninsufficient degree of deceleration. Thus, it is desirable in the greatacceleration range C to set the downshift correction factor DDSRDN muchgreater than the values set in direct proportion to the vehicleacceleration.

The operation of the speed change control apparatus of the inventionwill be described in connection with a downhill slope having itsgradient changed, as shown in FIG. 15, to cause a vehicle accelerationchange when the vehicle is coasting with the accelerator pedal heldreleased. In this case, a stronger engine brake is required to deal witha great vehicle acceleration change at time t1. The invention meets thisrequirement by setting the acceleration flag VSPPLS at the point 160 ofFIG. 5 when the vehicle acceleration increases into the acceleratedmotion range (FIG. 12), calculating the down-shaft correction factorDDSRDN from the map, as shown in FIG. 13, at the point 170 of FIG. 6,and adding the correction factor DDSRDN to the corrected target inputspeed value DSRENBR at the point 204 of FIG. 7 since the acceleratorpedal remains released. As a result, the target input shaft speed DSRREVincreases by the correction factor DDSRDN at uniform intervals of time(5 msec). If the vehicle acceleration is in the intermediate or greatacceleration range B or C (FIG. 14), the rate of increase of the enginebraking force will increase according to the degree of vehicleacceleration.

Since the target input shaft speed DSRREV changes continuously atuniform time intervals by a down-shaft correction factor DDSRDN set toincrease at a greater vehicle acceleration, as shown in FIGS. 13 and 14,when the vehicle acceleration exceeds a predetermined threshold value,the engine brake force can change, in such a smooth manner as to meetthe operator's expectation, according to the vehicle accelerationchange, as shown in FIG. 15, with no sudden change even upon theoccurrence of a rapid and great vehicle acceleration change. It is,therefore, possible to permit the vehicle to coast smoothly on adownhill slope having a changing gradient with the accelerator pedalbeing released.

It is to be understood that the deceleration made with the use of thedown-shaft correction factor DDSRDN is not intended to reduce thevehicle acceleration to zero and to shift the vehicle acceleration fromthe accelerated motion range to the uniform motion range (FIG. 12).

When the vehicle acceleration is in the small acceleration range A (FIG.14), the down-shaft correction factor DDSRDN is zero or almost zero.Thus, the target input shaft speed DSRREV is held almost unchanged sothat the vehicle can coast down the hill without engine brakeapplication. This is effective to provide a comfortable driving feel tothe operator.

It has been discovered through experiments that the degree ofdeceleration the operator expects when the accelerator pedal is releasedremains about 0.06 G (acceleration=−0.0.6 G) and it is almostindependent on the vehicle speed VSP, as shown in FIG. 17. If thedeceleration is set at 0.06 G regardless of vehicle speed, however, theoperator will bodily sense a stronger engine brake force at certain lowvehicle speeds and an insufficient engine brake force at certain highvehicle speeds. For this reason, it is desirable to change the targetdeceleration according to the operators bodily sensation of thedeceleration. That is, at certain low vehicle speeds, the targetdeceleration is reduced below 0.06 G. At certain high vehicle speeds,the rate of change of the deceleration is increased to change the enginebrake force continuously to bring the vehicle acceleration into theuniform motion range (FIG. 12) with the accelerator pedal beingdepressed.

The calculation of the up-shift correction factor DDSRUP will bedescribed further with reference to FIG. 17. The bold lines indicatechanges in the up-shaft correction factor DDSRUP in connection withvalues set in direct proportion to the vehicle acceleration(deceleration), as indicated by the broken line. FIG. 17 shows thedeceleration region where the vehicle acceleration is negative asdivided into a small deceleration range A where the vehicle decelerationis less than a predetermined value near zero, an intermediatedeceleration range B and a great deceleration range C. The smalldeceleration range A is characterized by the fact that the operator isbothered with frequent engine speed (target input shaft speed) changes,the operator feels a sense of incompatibility with the up-shiftcorrection factor DDSRUP set in direct proportion to the vehicleacceleration, indicated by the broken line of FIG. 17, and the operatordoes not expect vehicle deceleration even when the accelerator pedal isreleased. Thus, it is desirable in the small acceleration range A to setthe up-shift correction factor DDSRUP almost at zero. The vehicleacceleration (deceleration) comes into the intermediate decelerationrange B, for example, when the vehicle is coasting on a road changingfrom a downhill slope to a steep uphill slope. The intermediatedeceleration range B is characterized by the fact that the operatorfeels like the initiation of brake application and requires a rapidengine brake force decrease to retain the vehicle speed. The operatorwill be impatient with a delay of engine brake force decrease if theup-shift correction factor DDSRUP is set in direct proportion to thevehicle deceleration, as indicated by the broken line of FIG. 17. Thus,it is desirable in the intermediate deceleration range B to increase therate of reduction of the engine brake force and thereafter decrease theengine brake force at a rate less than the gradient of the broken lineof FIG. 17 by setting the absolute value of the up-shift correctionfactor DDSRUP at a great value according to the vehicle deceleration andthen correct the up-shift correction factor DDSRUP at a rate smallerthan the rate of change of the factor calculated in direct proportionthe vehicle deceleration. In the great deceleration range C, theup-shift correction factor DDSRUP is set substantially at a constantvalue or at a value decreasing at a very small rate according to thevehicle deceleration. As shown in FIG. 17. the absolute value of theup-shift correction factor DDSRUP is less than the factor calculated indirect proportion to the vehicle deceleration, as indicated by thebroken line of FIG. 17.

The operation of the speed change control apparatus of the inventionwill be described in connection with a vehicle coasting on a roadchanging from a downhill slope to an uphill slope, as shown in FIG. 18.In this case, a rapid engine brake force decrease is required to dealwith a rapid vehicle deceleration increase at time t1. The inventionmeets this requirement by setting the deceleration flag VSPMS at thepoint 164 of FIG. 5 when the vehicle deceleration increases into thedecelerated motion range (FIG. 12), calculating the up-shaft correctionfactor DDSRUP from the map, as shown in FIG. 13, at the point 172 ofFIG. 6, and adding the correction factor DDSRUP to the corrected targetinput speed value DSRENBR at the point 216 of FIG. 7 since theaccelerator pedal remains released and the brake pedal is released; As aresult, the target input shaft speed DSRREV decreases by the correctionfactor DDSRUP at uniform intervals of time (5 msec). If the vehicledeceleration is in the intermediate or great deceleration range B or C(FIG. 17), the rate of decrease of the engine braking force willincrease according to the degree of vehicle deceleration.

Since the target input shaft speed DSRREV changes continuously atuniform time intervals by an up-shaft correction factor DDSRUP set todecreases at a greater vehicle deceleration, as shown in FIGS. 13 and17, when the vehicle deceleration exceeds a predetermined thresholdvalue, the engine brake force can change, in such a smooth manner as tomeet the operator's expectation, according to the vehicle decelerationchange, as shown in FIG. 18, with no sudden change even upon theoccurrence of a rapid and great vehicle deceleration change. It is,therefore, possible to permit the vehicle to coast smoothly on a roadchanging from a downhill slope to a steep uphill slope.

What is claimed is:
 1. An apparatus for controlling a continuouslyvariable transmission for use with an automotive vehicle including anaccelerator pedal, the transmission having an input and output shaft,the transmission being operable at a variable speed ratio fortransmitting a drive from the input shaft to the output shaft,comprising: means for sensing vehicle operating conditions includingvehicle acceleration; means for producing a released accelerator pedalindicative signal when the accelerator pedal is released; means forcalculating a target value for the speed of rotation of the input shaftbased on the sensed vehicle operating conditions; means for calculatinga correction factor per predetermined unit time based on the sensedvehicle acceleration when the sensed vehicle acceleration exceeds athreshold value in the presence of the released accelerator pedalindicative signal; means for adding the correction factor to the targetinput shaft speed value to correct the target input shaft speed value atintervals of the predetermined unit time; and means for controlling thespeed ratio to bring the input shaft speed into coincidence with thecorrected target value.
 2. A continuously variable transmission controlapparatus as claimed in claim 1, further including means for reducingthe correction factor substantially to zero when the vehicleacceleration is equal to or less than a predetermined value.
 3. Acontinuously variable transmission control apparatus as claimed in claim1, further including means for increasing the correction factor based onthe vehicle acceleration.
 4. A continuously variable transmissioncontrol apparatus as claimed in claim 3, further including means forreducing the correction factor substantially to zero when the vehicleacceleration is equal to or less than a predetermined value.
 5. Anapparatus for controlling a continuously variable transmission for usewith an automotive vehicle including an accelerator pedal, thetransmission having an input and output shaft, the transmission beingoperable at a variable speed ratio for transmitting a drive from theinput shaft to the output shaft, comprising: means for sensing vehicleoperating conditions including vehicle deceleration; means for producinga released accelerator pedal indicative signal when the acceleratorpedal is released; means for calculating a target value for the speed ofrotation of the input shaft based on the sensed vehicle operatingconditions; means for calculating a correction factor per predeterminedunit time based on the sensed vehicle deceleration when the sensedvehicle deceleration exceeds a first threshold value in the presence ofthe released accelerator pedal indicative signal; means for subtractingthe correction factor from the target input shaft speed value todecrease the target input shaft speed value at intervals of thepredetermined unit time; and means for controlling the speed ratio tobring the input shaft speed into coincidence with the decreased targetvalue.
 6. A continuously variable transmission control apparatus asclaimed in claim 5, further including means for reducing the correctionfactor substantially to zero when the vehicle deceleration is equal toor less than a predetermined value.
 7. A continuously variabletransmission control apparatus as claimed in claim 5, further includingmeans for increasing the absolute value of the correction factor basedon the vehicle deceleration.
 8. A continuously variable transmissioncontrol apparatus as claimed in claim 7, further including means forreducing the correction factor substantially to zero when the vehicledeceleration is equal to or less than a predetermined value.
 9. Acontinuously variable transmission control apparatus as claimed in claim5, further including means for setting the correction factor at aconstant value regardless of the vehicle deceleration when the vehicledeceleration exceeds a second threshold value having an absolute valuegreater than that of the first threshold value.
 10. A method ofcontrolling a continuously variable transmission for use with anautomotive vehicle including an accelerator pedal, the transmissionhaving an input and output shaft, the transmission being operable at avariable speed ratio for transmitting a drive from the input shaft tothe output shaft, the method comprising the steps of: sensing vehicleoperating conditions including vehicle acceleration; producing areleased accelerator pedal indicative signal when the accelerator pedalis released; calculating a target value for the speed of rotation of theinput shaft based on the sensed vehicle operating conditions;calculating a correction factor based on the sensed vehicle accelerationwhen the sensed vehicle acceleration exceeds a threshold value in thepresence of the released accelerator pedal indicative signal; adding thecorrection factor to the target input shaft speed value to correct thetarget input shaft speed value; controlling the speed ratio to bring theinput shaft speed into coincidence with the corrected target value; andcontinuously repeating the above sequence of steps at uniform intervalsof time to effect changes in the target input shaft speed value inresponse to changes in the vehicle acceleration.
 11. A method forcontrolling a continuously variable transmission in accordance withclaim 10, wherein the step of calculating a correction factor includesthe step of reducing the correction factor substantially to zero whenthe vehicle acceleration is equal to or less than a predetermined value.12. A method for controlling a continuously variable transmission inaccordance with claim 11, wherein the step of calculating a correctionfactor includes the step of increasing the correction factor based onthe vehicle acceleration.
 13. A method for controlling a continuouslyvariable transmission in accordance with claim 10, wherein the step ofcalculating a correction factor includes the step of reducing thecorrection factor substantially to zero when the vehicle acceleration isequal to or less than a predetermined value.
 14. A method of controllinga continuously variable transmission for use with an automotive vehicleincluding an accelerator pedal, the transmission having an input andoutput shaft, the transmission being operable at a variable speed ratiofor transmitting a drive from the input shaft to the output shaft, themethod comprising the steps of: sensing vehicle operating conditionsincluding vehicle deceleration; producing a released accelerator pedalindicative signal when the accelerator pedal is released; calculating atarget value for the speed of rotation of the input shaft based on thesensed vehicle operating conditions; calculating a correction factorbased on the sensed vehicle deceleration when the sensed vehicleacceleration exceeds a first threshold value in the presence of thereleased accelerator pedal indicative signal; subtracting the correctionfactor to the target input shaft speed value to decrease the targetinput shaft speed value; controlling the speed ratio to bring the inputshaft speed into coincidence with the decreased target value; andcontinuously repeating the above sequence of steps at uniform intervalsof time to effect changes in the target input shaft speed value inresponse to changes in the vehicle deceleration.
 15. A method forcontrolling a continuously variable transmission in accordance withclaim 14, wherein the step of calculating a correction factor includesthe step of reducing the correction factor substantially to zero whenthe vehicle deceleration is equal to or less than a predetermined value.16. A method for controlling a continuously variable transmission inaccordance with claim 15, wherein the step of calculating a correctionfactor includes the step of increasing the absolute value of thecorrection factor based on the vehicle deceleration.
 17. A method forcontrolling a continuously variable transmission in accordance withclaim 14, wherein the step of calculating a correction factor includesthe step of reducing the correction factor substantially to zero whenthe vehicle deceleration is equal to or less than a predetermined value.18. A method for controlling a continuously variable transmission inaccordance with claim 14, wherein the step of calculating a correctionfactor includes the step of setting the correction factor at a constantvalue regardless of the vehicle deceleration when the vehicledeceleration exceeds a second threshold value having an absolute valuegreater than that of the first threshold value.
 19. An apparatus forcontrolling a continuously variable transmission for use with anautomotive vehicle including an accelerator pedal, the transmissionhaving an input and output shaft, the transmission being operable at avariable speed ratio for transmitting a drive from the input shaft tothe output shaft, comprising: means for sensing vehicle operatingconditions including vehicle speed; means for calculating a target valuefor the speed of rotation of the input shaft based on the sensed vehicleoperating conditions; means for producing a released accelerator pedalindicative signal when the accelerator pedal is released; means fordetermining a vehicle acceleration; means for calculating a correctionfactor per predetermined unit time based on the determined vehicleacceleration when the determined vehicle acceleration exceeds athreshold value in the presence of the released accelerator pedalindicative signal; means for adding the correcting factor to the targetinput shaft speed value to correct the target input shaft speed value atintervals of the predetermined unit time; and means for controlling thespeed ratio to bring the input shaft speed into coincidence with thecorrected target value.
 20. A continuously variable transmission controlapparatus as claimed in claim 19, further including means for reducingthe correction factor substantially to zero when the vehicleacceleration is equal to or less than a predetermined value.
 21. Acontinuously variable transmission control apparatus as claimed in claim19, further including means for increasing the corrector factor with theincrease of the vehicle acceleration.
 22. A continuously variabletransmission control apparatus as claimed in claim 21, further includingmeans for reducing the correction factor substantially to zero when theabsolute value of the vehicle acceleration is equal to or less than apredetermined value.
 23. An apparatus for controlling a continuouslyvariable transmission for use with an automotive vehicle including anaccelerator pedal, the transmission having an input and output shaft,the transmission being operable at a variable speed ratio fortransmitting a drive from the input shaft to the output shaft,comprising: means for sensing vehicle operating conditions includingvehicle speed; means for calculating a target value for the speed ofrotation of the input shaft based on the sensed vehicle operatingconditions; means for producing a released accelerator pedal indicativesignal when the accelerator pedal is released; means for determining avehicle deceleration; means for calculating a correction factor perpredetermined unit time based on the determined vehicle decelerationwhen the determined vehicle deceleration exceeds a first threshold valuein the presence of the released accelerator pedal indicative signal;means for subtracting the correction factor from the target input shaftspeed value to decrease the target input shaft speed value at intervalsof the predetermined unit time; and means for controlling the speedratio to bring the input shaft speed into coincidence with the decreasedtarget value.
 24. A continuously variable transmission control apparatusas claimed in claim 23, further including means for reducing thecorrection factor substantially to zero when the vehicle deceleration isequal to or less than a predetermined value.
 25. A continuously variabletransmission control apparatus as claimed in claim 23, further includingmeans for increasing the absolute value of the correction factor basedon the vehicle deceleration.
 26. A continuously variable transmissioncontrol apparatus as claimed in claim 25, further including means forreducing the correction factor substantially to zero when the vehicledeceleration is equal to or less than a predetermined value.
 27. Acontinuously variable transmission control apparatus as claimed in claim23, further including means for setting the correction factor at aconstant value regardless of the vehicle deceleration when the vehicledeceleration exceeds a second threshold value having an absolute valuegreater than that of the first threshold value.
 28. A method ofcontrolling a continuously variable transmission for use with anautomotive vehicle including an accelerator pedal, the transmissionhaving an input and output shaft, the transmission being operable at avariable speed ratio for transmitting a drive from the input shaft tothe output shaft, the method comprising the steps of: sensing vehicleoperating conditions including vehicle speed; calculating a target valuefor the speed of rotation of the input shaft based on the sensed vehicleoperating conditions; producing a released accelerator pedal indicativesignal when the accelerator pedal is released; determining a vehicleacceleration; calculating a correction factor based on the determinedvehicle acceleration when the determined vehicle acceleration exceeds athreshold value in the presence of the released accelerator pedalindicative signal; adding the correction factor to the target inputshaft speed value to correct the target input shaft speed value;controlling the speed ratio to bring the input shaft speed intocoincidence with the corrected target value; and continuously repeatingthe above sequence of steps at uniform intervals of time to effectchanges in the target input shaft speed value in response to changed inthe vehicle acceleration.
 29. A method for controlling a continuouslyvariable transmission in accordance with claim 28, wherein the step ofcalculating a correction factor includes the step of reducing thecorrection factor substantially to zero when the vehicle acceleration isequal to or less than a predetermined value.
 30. A method forcontrolling a continuously variable transmission in accordance withclaim 29, wherein the step of calculating a correction factor includesthe step of increasing the correction factor based on the vehicleacceleration.
 31. A method for controlling a continuously variabletransmission in accordance with claim 28, wherein the step ofcalculating a correction factor includes the step of reducing thecorrection factor substantially to zero when the vehicle acceleration isequal to or less than a predetermined value.
 32. A method of controllinga continuously variable transmission for use with an automotive vehicleincluding an accelerator pedal, the transmission having an input andoutput shaft, the transmission being operable at a variable speed ratiofor transmitting a drive from the input shaft to the output shaft, themethod comprising the steps of: sensing vehicle operating conditionsincluding vehicle speed; calculating a target value for the speed ofrotation of the input shaft based on the sensed vehicle operatingconditions; producing a released accelerator pedal indicative signalwhen the accelerator pedal is released; determining a vehicledeceleration; calculating a correction factor based on the determinedvehicle deceleration when the determined vehicle deceleration exceeds afirst threshold value in the presence of the released accelerator pedalindicative signal; subtracting the correction factor to the target inputshaft speed value to decrease the target input shaft speed value;controlling the speed ratio to bring the input shaft speed intocoincidence with the corrected target value; and continuously repeatingthe above sequence of steps of uniform intervals of time to effectchanges in the target input shaft speed value in response to changes inthe vehicle deceleration.
 33. A method for controlling a continuouslyvariable transmission in accordance with claim 32, wherein the step ofcalculating a correction factor includes the step of reducing thecorrection factor substantially to zero when the vehicle deceleration isequal to or less than a predetermined value.
 34. A method forcontrolling a continuously variable transmission in accordance withclaim 33, wherein the step of calculating a correction factor includesthe step of increasing the absolute value of the correction factor basedon the vehicle deceleration.
 35. A method for controlling a continuouslyvariable transmission in accordance with claim 32, wherein the step ofcalculating a correction factor includes the step of reducing thecorrection factor substantially to zero when the vehicle deceleration isequal to or less than a predetermined value.
 36. A method forcontrolling a continuously variable transmission in accordance withclaim 32, wherein the step of calculating a correction factor includesthe step of setting the correction factor at a constant value regardlessof the vehicle deceleration when the vehicle deceleration exceeds asecond threshold value having an absolute value greater than that of thefirst threshold value.